From 816552e7354cd4bc07cac1e5862fb7dc934eac1b Mon Sep 17 00:00:00 2001
From: slhx agent <slhx@users.noreply.github.com>
Date: Mon, 11 May 2026 07:59:32 +0200
Subject: [PATCH] feat(runtime): support slhx drag drops

req: htmx_equivalents/002

req: dx/008

req: list/003

req: examples/001
---
 examples/techdemo/README.md                   |  2 +-
 examples/techdemo/src/main.rs                 | 37 +++----------------
 .../templates/partials/issue_card.heml        |  2 +-
 .../templates/partials/issue_lane.heml        |  2 +-
 slhx-js/runtime/slhx.js                       | 22 +++++++++--
 slhx-js/tests/runtime.rs                      | 12 ++++++
 6 files changed, 39 insertions(+), 38 deletions(-)

diff --git a/examples/techdemo/README.md b/examples/techdemo/README.md
index 4e1c86d..0e79b6c 100644
--- a/examples/techdemo/README.md
+++ b/examples/techdemo/README.md
@@ -17,7 +17,7 @@ This is a polished Linear-style product demo for planning typed work across lane
 - root-scoped runtime lowering (`data-hid`, `data-sid`)
 - page-enhancer navigation with native link fallback
 - SSE server push into a generated slot
-- drag-and-drop lane moves persisted by typed server handlers
+- drag-and-drop lane moves persisted by typed server handlers through the slhx runtime
 
 Verification:
 
diff --git a/examples/techdemo/src/main.rs b/examples/techdemo/src/main.rs
index 753027e..965d9e9 100644
--- a/examples/techdemo/src/main.rs
+++ b/examples/techdemo/src/main.rs
@@ -367,44 +367,17 @@ fn shell(body: String) -> String {
   <title>slhx Techdemo</title>
   <script src="/slhx.js" defer></script>
   <script>
-    function slhxTechdemoEffect(root, data) {{
+    function slhxTechdemoLaunch(button) {{
+      const form = button.closest('form');
+      const data = new URLSearchParams(new FormData(form));
+      data.set('__h', button.getAttribute('data-hid'));
       fetch('/', {{
         method: 'POST',
         headers: {{ 'Content-Type': 'application/x-www-form-urlencoded;charset=UTF-8', 'Accept': 'application/slhx' }},
         body: data
       }})
       .then((response) => response.arrayBuffer())
-      .then((buffer) => window.slhx.applyBatch(buffer, root));
-    }}
-    function slhxTechdemoLaunch(button) {{
-      const form = button.closest('form');
-      const data = new URLSearchParams(new FormData(form));
-      data.set('__h', button.getAttribute('data-hid'));
-      slhxTechdemoEffect(button.closest('[data-slhx-root]'), data);
-      return false;
-    }}
-    function slhxTechdemoDrag(event) {{
-      event.dataTransfer.effectAllowed = 'move';
-      event.dataTransfer.setData('text/plain', event.currentTarget.getAttribute('data-key'));
-    }}
-    function slhxTechdemoDragOver(event) {{
-      event.preventDefault();
-      event.currentTarget.classList.add('drop-ready');
-    }}
-    function slhxTechdemoDragLeave(event) {{
-      event.currentTarget.classList.remove('drop-ready');
-    }}
-    function slhxTechdemoDrop(event) {{
-      event.preventDefault();
-      const lane = event.currentTarget;
-      lane.classList.remove('drop-ready');
-      const id = event.dataTransfer.getData('text/plain');
-      if (!id) return false;
-      const data = new URLSearchParams();
-      data.set('__h', lane.getAttribute('data-move-hid'));
-      data.set('work_id', id);
-      data.set('lane', lane.getAttribute('data-lane'));
-      slhxTechdemoEffect(lane.closest('[data-slhx-root]'), data);
+      .then((buffer) => window.slhx.applyBatch(buffer, button.closest('[data-slhx-root]')));
       return false;
     }}
   </script>
diff --git a/examples/techdemo/templates/partials/issue_card.heml b/examples/techdemo/templates/partials/issue_card.heml
index ec2edb1..203487f 100644
--- a/examples/techdemo/templates/partials/issue_card.heml
+++ b/examples/techdemo/templates/partials/issue_card.heml
@@ -1,4 +1,4 @@
-<article +class="self.class" +data-key="self.id" draggable="true" ondragstart="slhxTechdemoDrag(event)">
+<article +class="self.class" +data-key="self.id" draggable="true">
   <header><strong>{+ self.title +}</strong><span class="pill">{+ self.stage +}</span></header>
   <div class="impact"><i +style="self.impact_style"></i></div>
   <div class="card-actions">
diff --git a/examples/techdemo/templates/partials/issue_lane.heml b/examples/techdemo/templates/partials/issue_lane.heml
index 0203320..5b07665 100644
--- a/examples/techdemo/templates/partials/issue_lane.heml
+++ b/examples/techdemo/templates/partials/issue_lane.heml
@@ -1,4 +1,4 @@
-<section +class="self.class" +data-lane="self.lane_id" +data-move-hid="self.move_handle" ondragover="slhxTechdemoDragOver(event)" ondragleave="slhxTechdemoDragLeave(event)" ondrop="slhxTechdemoDrop(event)">
+<section +class="self.class" +data-lane="self.lane_id" +data-hid="self.move_handle" data-slhx-on="drop">
   <h3>{+ self.title +}</h3>
   <p>{+ self.description +}</p>
   <template h-for="card in &self.cards">
diff --git a/slhx-js/runtime/slhx.js b/slhx-js/runtime/slhx.js
index 8041874..287b97e 100644
--- a/slhx-js/runtime/slhx.js
+++ b/slhx-js/runtime/slhx.js
@@ -10,6 +10,7 @@
   const timers = new WeakMap();
   const sseSources = new WeakMap();
   const atomStores = new WeakMap();
+  const dragKeys = new WeakMap();
 
   function roots() {
     return Array.from(document.querySelectorAll(`[${ROOT}]`));
@@ -51,11 +52,13 @@
     }
   }
 
-  function formDataFor(el) {
+  function formDataFor(el, eventName) {
     const form = el.tagName === "FORM" ? el : el.closest("form");
     const data = form ? new FormData(form) : new FormData();
     const id = handleId(el) || (form && handleId(form));
     if (id && !data.has("__h")) data.set("__h", id);
+    const dragKey = eventName === "drop" && dragKeys.get(rootOf(el));
+    if (dragKey && !data.has("work_id")) data.set("work_id", dragKey);
     for (const { name, value } of Array.from(el.attributes || [])) {
       if (name.startsWith("data-") && !name.startsWith("data-slhx-") && name !== HID && name !== SID) {
         data.set(name.slice(5).replace(/-/g, "_"), value);
@@ -85,7 +88,7 @@
 
   async function send(el, eventName) {
     if (el.getAttribute("data-slhx-confirm") && !confirm(el.getAttribute("data-slhx-confirm"))) return;
-    const { form, data, multipart } = formDataFor(el);
+    const { form, data, multipart } = formDataFor(el, eventName);
     const target = form || el;
     const policy = requestPolicy(target, eventName);
     const active = pending.get(target);
@@ -386,8 +389,21 @@
   }
 
   function bindRoot(root) {
-    ["click", "submit", "input", "change"].forEach((name) => {
+    ["click", "submit", "input", "change", "dragstart", "dragover", "drop"].forEach((name) => {
       root.addEventListener(name, (event) => {
+        if (name === "dragstart") {
+          const item = closestInRoot(event.target, root, "[data-key]");
+          if (item) {
+            dragKeys.set(root, item.getAttribute("data-key"));
+            if (event.dataTransfer) event.dataTransfer.setData("text/plain", item.getAttribute("data-key"));
+          }
+          return;
+        }
+        if (name === "dragover") {
+          const drop = closestInRoot(event.target, root, `[${HID}][data-slhx-on="drop"]`);
+          if (drop) event.preventDefault();
+          return;
+        }
         const nav = closestInRoot(event.target, root, "a[data-slhx-nav], [data-slhx-boost] a[href]");
         if (name === "click" && nav && sameOriginNav(event, nav)) {
           event.preventDefault();
diff --git a/slhx-js/tests/runtime.rs b/slhx-js/tests/runtime.rs
index a9eae39..8ada1d5 100644
--- a/slhx-js/tests/runtime.rs
+++ b/slhx-js/tests/runtime.rs
@@ -27,6 +27,18 @@ fn runtime_clicking_submitter_schedules_form_submit() {
     assert!(source.contains("schedule(form, \"submit\")"));
 }
 
+#[test]
+fn runtime_supports_drag_drop_params_without_user_js() {
+    // req: htmx_equivalents/002, req: dx/008
+    let source = slhx_js::RUNTIME_JS;
+
+    assert!(source.contains("const dragKeys = new WeakMap()"));
+    assert!(source.contains("dragstart"));
+    assert!(source.contains("dragover"));
+    assert!(source.contains("eventName === \"drop\""));
+    assert!(source.contains("data.set(\"work_id\", dragKey)"));
+}
+
 #[test]
 fn runtime_supports_queued_request_policy() {
     let source = slhx_js::RUNTIME_JS;